Vehicular tires, particularly pneumatic tires, are sometimes provided with a component such as, for example, a tread which is comprised of a rubber composition which contains silica, particularly amorphous precipitated silica, reinforcement.
Typically the rubber composition of the component also contains a coupling agent to aid in enhancing the reinforcing effect of the silica for the respective elastomer(s) of the rubber composition such as, for example, a tire tread. The use of coupling agents for such purpose is well known to those having skill in such art.
Elastomer blends which contain, for example, cis 1,4-polybutadiene and styrene/butadiene elastomers are often used for such tire component (e.g. tire tread). Rubber compositions may also contain various amounts of additional diene-based elastomers such as, for example, one or more of cis 1,4-polyisoprene, cis 1,4-polybutadiene, medium vinyl polybutadiene, styrene/butadiene copolymers, isoprene/butadiene copolymers, and minor amounts of 3,4-polyisoprene.
For the above mentioned styrene/butadiene copolymer rubber, both emulsion polymerization prepared and organic solvent polymerization prepared styrene/butadiene copolymer elastomers have been used. Also, historically, emulsion polymerization derived terpolymer elastomers comprised of units derived from styrene and 1,3-butadiene together with an additional monomer have been prepared and proposed for use for various products.
For example, according to U.S. Pat. No. 5,902,852, it has been proposed to modify asphalt cement with a rubbery terpolymer prepared by emulsion polymerization which is comprised of repeat units derived from conjugated diolefin monomer, such as, for example, cis 1,4-polybutadiene, vinyl aromatic monomer such as styrene and a small amount of hydroxypropyl methacrylate (HPMA).
For example, hydroxy-containing polymers and silica are variously disclosed in U.S. Pat. Nos. 4,150,014, 4,150,015, 4,152,308 and 4,357,432. However it is not seen that it was contemplated to include an alkoxysilane/polysulfide silica coupler in such blends and which is considered herein to present the above problem of relatively large Mooney viscosity increase of such a mixture within an internal rubber mixer.
In the description of this invention, the terms “rubber” and “elastomer” if used herein, may be used interchangeably, unless otherwise prescribed. The terms “rubber composition”, “compounded rubber” and “rubber compound”, if used herein, are used interchangeably to refer to “rubber which has been blended or mixed with various ingredients and materials” and such terms are well known to those having skill in the rubber mixing or rubber compounding art.
The term “phr” if used herein, and according to conventional practice, refers to “parts of a respective material per 100 parts by weight of rubber, or elastomer”.
The Tg of an elastomer, if referred to herein, refers to a “glass transition temperature” of the elastomer which can conveniently be determined by a differential scanning calorimeter at a heating rate of 10° C. per minute.